1. Field of the Invention
This invention relates to a process for producing a color filter which can be used in color solid state image pick-up devices, contact type image sensors and color displays such as CCD (charge coupled device), BBD (bucket brigade device,), CID (charge injection device), BASIS (base store type image sensor), etc.
2. Related Backgroud Art
As a color filter, there has been known a dyed color filter which is prepared by providing a mordant layer comprising a hydrophilic polymeric material on a substrate and dyeing the mordant layer with a dye to provide a colored layer. However, this kind of color filter has the following disadvantages:
(1) A mordant layer is required.
(2) An intermediate layer for prevention of staining is required to be provided on the mordant layer for preventing the adjacent colorant layers from color mixing.
(3) Since color formation is effected by dyeing of the mordant layer, the thickness of the layer is necessarily required to be thick.
(4) Dyeing with a dye is susceptible to fading on account of insufficient humidity resistance, light resistance of the colored layer.
As a color filter of another system free from these disadvantages, there is one in which the colorant layer is formed, for example, as the vapor deposited thin film of a colorant by vacuum vapor deposition. As a method for producing this kind of color filter, the so called reverse etching method (or the lift-off method), which comprises forming a dissolvable photoresist pattern on a substrate, then forming a colorant layer, subsequently removing the dissolvable resist pattern therebeneath by dissolution, thereby liberating off the unnecessary colorant layer formed as the upper layer thereon at the same time, has been known as disclosed in Japanese Patent Publication No. 16815/1972. According to the reverse etching method, after a pattern resist which is negative relative to the colorant layer of a desired shape has been provided by use of a material dissolvable layer, primarily a positive-type resist, a colorant layer is provided according to, for example, the vacuum vapor deposition method, followed by dissolution of the resist pattern of the lower layer, to provide a colored pattern of a desired shape. According to this method, since a colored pattern consisting only of a colorant layer can be obtained, the constitution can be advantageously simple.
The method for formation of a color filter comprising the three colors of blue, green and red by the reverse etching method is outlined below by referring to FIGS. 9A-9D.
A substrate 1 is coated with a photosensitive resin (photoresist) 2 thereon and, by use of a mask having a light-transmitting portion of a desired shape, the photoresist 2 laminated on the substrate 1 is subjected to pattern exposure, and a photoresist pattern of a desired shape is formed by dissolving the exposed portion (when the photoresist is a positive-type). This state is shown as a schematic sectional view in FIG. 9A. FIG. 9B shows the state in which a blue colorant layer 3 is provided on the whole surface according to the vacuum vapor deposition method, etc. Subsequently, when the resist pattern 2 remaining on the substrate 1 is dissolved with a removing liquid, the colorant layer on the resist pattern 2 is also liberated off to give a blue colorant layer pattern 4 as shown in FIG. 9C.
By repeating the above steps for the colorants of green and red, a color filter having the tricolor colorant layer patterns 4, 5 and 6 as shown in FIG. 9D can be formed.
Exposure in the steps of forming the respective colorant layer patterns is effected generally after moving horizontally the one mask as described above to a desired position. Accordingly, as shown in FIG. 10, the alignment mark 7a of the mask 7 is required to be coincident with the alignment mark 1a marked on the substrate 1 before practicing every exposure, and therefore a plural number of alignment marks 1a is required to be marked on the substrate 1.
Since the alignment marks 1a on the substrate 1 are required to be marked with high positional precision, they have been conventionally formed according to the dry etching method. This dry etching method is shown in FIGS. 11A-11D. First, on the substrate 1, a metal layer 8 such as of Al, Cr, etc. is formed by vapor deposition (FIG. 11A), and after coating of a photoresist 2 on the whole surface thereof (FIG. 11B), patterning of said photoresist 2 is effected and a portion of the metal layer 8 not covered with the resist pattern 2a is subjected to dry etching (FIG. 11C), and thereafter the resist pattern 2a on the remaining metal layer 8 is removed to mark the desired alignment mark 1a (FIG. 11D).
By formation of alignment marks in this manner, the following problems will ensue.
1. A metal is first vapor deposited to the broad area of the substrate 1, and then unnecessary portion of the metal is removed. Therefore, the unnecessary portion of the vapor deposited metal cannot be completely dry etched to leave attached matters to remain on the substrate and, when a colorant layer is laminated thereon, adhesion between the colorant layer and the substrate is worsened to result in peel-off of the colorant and give rise to appearance defects, thus causing lowering in yield.
2. Since a metal alignment mark is required to be formed previously before vapor deposition of a colorant layer, enormous amounts material cost, installation cost and labor are needed for preparation of metal alignment mark, and the production cost of a color filter is increased.